Using water with fluoride significantly reduces tooth decay, even if that use didn’t start until adulthood, according to a new study by a professor at UNC-Chapel Hill.

The study examined dental records of 3,779 older teens and adults who had spent various amounts of time living in communities with fluoridated water supplies.

“We found there are protective effects for adults and, equally important, that the protection occurs even if those adults didn’t have access to fluoridated water when they were children,” said Gary Slade, director of the oral epidemiology Ph.D. program at the UNC-Chapel Hill School of Dentistry.

Slade said many people think of tooth decay as a childhood issue, but adults are equally vulnerable. Today’s adults with good dental health may have long years of living with fluoridated water supplies to thank, he said.

Fluoride is a mineral occurring naturally in the earth that strengthens tooth enamel. It is often added to toothpaste and dental rinses, but it’s the day-to-day use of fluoridated water that has been shown to have the greatest impact on dental health.

According to the Campaign for Dental Health, a coalition of dental and health groups, tooth loss among people ages 65 and older has dropped by 21 percent since 1961, when fluoridation was widely introduced.

Slade was working in Australia when he began the study in the late 1990s. He and other researchers from the University of Adelaide traced dental histories of their subjects – all Australians ages 15 and older – back to 1963.

Australia had little fluoridation in the early 1960s, but by 1980 two-thirds of the country had fluoridated water supplies, Slade said.

“So it was almost a natural survey,” he said.

The results showed that adults spending more than 75 percent of their lives in communities with fluoridated water had about 30 percent less tooth decay than those living for the same duration in areas without treated water, Slade said.

The research findings were published last week in the online Journal of Dental Research.

Fluoride has been used in public water supplies for more than 60 years, according to the federal Centers for Disease Control, which lists water fluoridation as one of the 10 greatest public health achievements of the 20th century.

Lisa Ward, communications director for the N.C. Dental Society, said about 80 percent of North Carolinians have access to fluoridated water.

Opponents of fluoridation sometimes argue that the process causes cancer or poses other health threats, but in 50 years of regular use, no such threats have emerged, Ward said. A 2011 a study approved by the National Cancer Institute found no link between bone cancer and fluoride, as had been alleged.

“In my estimation, and in the estimation of scientists, the opponents are using flawed data,” Ward said.

One potential side effect of fluoride is fluorosis, a staining of the teeth, Slade said. But this condition is not likely to occur with the levels of fluoride used in water systems, typically .7 to 1 parts per million, he said.

Slade said other studies have shown that adults ought to think twice before eschewing tap water in favor of bottled or filtered water.

“Some studies are beginning to show that people who choose bottled water as their predominate form of water, even if they are living in fluoridated areas, are losing the benefits,” he said.